Apparatus for making water skis

ABSTRACT

A pre-shaped aluminum plate is held against the flat end wall of an inverted mold cavity by vacuum pressure communicated through bore holes in the wall leading to a vacuum chamber in the mold body. A high temperature PTFE gasket shaped to match the plate fits in an annular recess in the wall to provide a seal between the wall and plate. Polyurethane foam expands and hardens in the mold cavity to further press the plate against the wall and to form a foamed plastic water ski having a flush aluminum deck. The mold cavity has a curved side wall to produce a ski having a radiused edge about the deck.

This application is a division, of application Ser. No. 431,845, filedSept. 30, 1982.

BACKGROUND OF THE INVENTION

This invention relates generally to an apparatus for making an articlehaving a foamed plastic body and a surface plate and more particularlyhas reference to an apparatus for making a polyurethane foam water skihaving a flush aluminum deck.

The current method for making foamed plastic water skis having aluminumdecks is described in U.S. Pat. No. 4,250,585, the disclosure of whichis incorporated herein by reference.

The patent describes a reaction injection molding process. A pluralityof rods are positioned in a mold cavity by plastic jigs. An aluminumsheet pre-treated to bond to foamed plastic is placed at the moldparting line to close the mold cavity. Foam is injected into the cavity,where it expands and hardens and bonds to the aluminum sheet. The skiblank is removed from the mold and the aluminum top surface is trimmedto the desired shape.

The known process has a number of disadvantages.

The requirement that the aluminum sheet be placed at the mold partingline limits ski design. The ski will necessarily have a flat top surfaceand will necessarily have a deck which lies on top of the foamed plasticbody. Those features detract from the safety and appearance of theproduct.

Another disadvantage is that costly and labor intensive production stepsare needed to trim the deck after molding. Those steps include bandsawtrimming of the aluminum deck top, routing the remaining edge material,and filing the edge for smoothness. The trimming steps also increase thelikelihood of product damage during manufacture.

A need thus exists for an apparatus in which a die cut aluminum ski topcan be placed in the mold cavity, thereby eliminating all product designlimitations and reducing the labor required to trim the ski top.

One obstacle which has heretofore prevented fulfillment of that need isthe extreme mold pressures which develop in reaction injection molding.The foam enters the mold in a liquid state. The foam then expandsrapidly to fill the mold cavity and produce a dense structural foambody. When attempting to place a pre-cut aluminum top in a mold cavity,a perfect seal must be maintained or the extreme mold pressures willcause the foam material to leak around and distort the aluminum top.

Pertinent U.S. and foreign patents are found in Class 264, subclasses46.4, 46.7, 46.8, 45.5 and Digest 83; Class 9, subclasses 310A, 310E and310R; Class 427, subclass 388.1 and Class 441, subclasses 68, 70 and 74of the official classifications of patents in the U.S. Patent andTrademark Office.

Examples of pertinent patents are U.S. Pat. Nos. 4,046,611; 4,261,778;2,920,898; 3,173,161; 3,318,609 and 3,928,106.

U.S. Pat. No. 4,046,611 shows a gasket, vacuum forming and polyurethanefoam blow molding. However, the patent does not use a plate and does notuse a gasket to prevent migration of the foam around the plate.

U.S. Pat. No. 4,261,778 shows a polyurethane foam ski construction.However, the patent does not show an inverted mold cavity, a gasket, ora vacuum-held plate.

The remaining patents are less pertinent and are cited merely to showthe state of the art in ski construction.

None of the patents fulfills the above-cited need for an apparatus inwhich a die cut aluminum ski top can be placed in the mold cavity.

SUMMARY OF THE INVENTION

The present invention overcomes the problems which exist in the priorart.

The present invention uses a vacuum to hold an aluminum ski top againstan upper wall of a mold cavity. Pins align the ski top in the mold. Ahigh temperature PTFE gasket which matches the shape of the precutaluminum ski top fits in a recess in the cavity above the edge of theski top. The vacuum draws the aluminum top upward, with its uppersurface periphery in tight sealing contact with the gasket. The mold isclosed and polyurethane foam is flowed into the mold. The materialexpands into dense foam, forcing the aluminum top even more tightlyagainst the upper wall of the cavity and against the gasket. An improvedski results in which the aluminum top is recessed in the body and thefoam tightly surrounds the edge of the top without flowing overperipheral areas of the top.

The present invention has several advantages over the prior art, namely,the elimination of three or four trimming steps in the productionprocess, a reduction in the number of blemishes and seconds in theproducts produced, and the ability to produce skis having somethingother than a flat top surface.

An object of the invention is to provide an apparatus for molding skiswherein a pre-cut aluminum sheet is positioned in the mold beforemolding and forms the top deck of the ski.

Yet another object of the invention is to provide an apparatus formaking a ski wherein post-molding trimming steps are eliminated.

A further object of the invention is to provide an apparatus for makinga ski having a rounded or radiused top edge.

Still another object of the invention is to provide an apparatus formaking a foamed plastic ski having a flush aluminum top deck.

Still another object of the invention is to provide a mold for making afoamed plastic ski having a vacuum chamber in communication withopenings in a mold cavity wall, whereby an aluminum plate or sheet usedto form the top deck of the ski is held against the cavity wall duringmolding by vacuum pressure.

Yet another object of the invention is to provide an apparatus that usesa high temperature PTFE gasket shaped to match the plate recessed in themold cavity wall for providing a seal between the plate and the wall.

Yet another object of the invention is to provide a mold having aninverted mold cavity with a flat end wall and a curved side wall.

Yet another object of the invention is to provide mold apparatuscomprising a mold body provided with an interior mold cavity and avacuum chamber, said mold cavity having a cavity wall provided with oneor more openings, and passageway means extending between the vacuumchamber and the mold cavity for establishing communication between saidvacuum chamber and said wall openings.

These and other and further objects and features of the invention areapparent in the discloure which includes the above and belowspecification and claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view, in section, of a known ski mold, showing thealuminum top positioned at the parting line of the mold.

FIG. 2 is a bottom view of an upper mold body embodying features of thepresent invention, showing an aluminum ski top positioned within themold cavity.

FIG. 3 is a sectional view taken along the Line 3--3 shown in FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a known ski mold is indicated generally by thenumeral 10. Details of the mold and of the method for using the mold toform a foam plastic water ski having an aluminum top deck are describedin the above-cited U.S. Pat. No. 4,250,585.

Briefly, the mold 10 has an elongated rectangular mold body 12 havingmold cavity 14 formed therein. The top surface of the mold body 12 formsa mold parting line 16. The cavity 14 extends downward into the body 12from the parting line 16. The curved base wall 18 of the cavity 14 isspaced from the base 20 of the mold body 12 and the slanted annular sidewall of the cavity 14 is spaced inward from the sides 24 of the moldbody 12.

An elongated rectangular aluminum sheet 26 is positioned on the partingline 16. The sheet 26 extends to the sides 24 of the mold body 12,thereby completely closing the open top end of the mold cavity 14. Thesheet 26 is pretreated to bond to foamed plastic.

Polyurethane foam is injected into the mold cavity 14 while the sheet 26is restrained. The foam expands to fill the cavity 14 and to come intocontact with the bottom surface of the sheet 26. The expanded foam isthen hardened into a dense polyurethane body having a cross sectionalshape identical to the cross sectional shape of the mold cavity 14. Thebottom surface of the aluminum sheet 26 bonds to the top surface of thepolyurethane body during the hardening process.

If desired, reinforcing elements can be placed in the cavity 14 prior toinjecting foam to produce a reinforced polyurethane body.

After hardening, the polyurethane body and aluminum sheet are removedfrom the mold body for finishing. It will be appreciated that thealuminum sheet 26 sits atop the polyurethane body and that peripheralportions of the sheet 26 overhang the peripheral edge of thepolyurethane body. In finishing, the overhanging portions of the sheet26 are sawed, routed and filed until the peripheral shape of the sheet26 is generally identical to the peripheral shape of the polyurethanebody.

The finished ski thus has a polyurethane body with slanted sides and acurved bottom and an aluminum deck extending completely across the topsurface of the polyurethane body. It will be appreciated that themolding process prevents the deck from being recessed in thepolyurethane body and from providing anything other than a flat topsurface on the ski.

The present invention provides an apparatus for making foamed plasticwater skis which overcome the limitations of the prior art.Specifically, the apparatus of the present invention eliminates thepost-molding trimming steps needed to form the top deck of the ski andis capable of producing skis having something other than a flat topsurface.

The preferred application of the apparatus of the present invention isin making a trick water ski having a radiused top area with an insetaluminum deck. The mold of the present invention described herein isuniquely adapted for practicing the process to make such a ski. It isunderstood, however, that the apparatus of the instant invention can beused to make many other products, such as slalom skis, combination pairsand knee boards, and that the mold described herein can be readilyadapted for use in such processes.

Referring to FIGS. 2 and 3, a mold useful in practicing the presentinvention is indicated generally by the numeral 28.

The mold 28 has a pair of separable elongated rectangular mold bodies 30and 32. The bodies 30 and 32 have abutting surfaces which define aparting line 34 of the mold 28.

One of the mold bodies 32 is provided with a mold cavity 36 and a vacuumchamber 38. The mold cavity 36 extends into the mold body 32 from theparting line 34. The curved annular sidewall 40 of the cavity 36 isspaced inward from the sides 42 of the mold body 32 and the flat basewall 44 of the cavity 36 is spaced inward from the base 46 of the moldbody 32. The vacuum chamber 38 is formed in the mold body 32 between themold cavity 36 and the base 46 of the mold body 32. A partition wall 48formed integrally with the mold body 32 separates the vacuum chamber 38from the mold cavity 36. The mold cavity 36 and vacuum chamber 38 arelongitudinally extended along the mold 32, as shown in FIG. 2.

In the preferred embodiment, the mold body 32 having the mold cavity 36and the vacuum chamber 38 forms the top of the mold 28 and the othermold body 30 forms the bottom of the mold 28. This provides an invertedmold cavity, i.e., a mold cavity which extends upwardly into the toppart of the mold and faces downwardly towards the bottom part of themold. It will be appreciated, however, that the bodies 30 and 32 can bereversed so that the mold body 32 having the mold cavity 36 and thevacuum chamber 38 would form the bottom part of the mold 28 and providea non-inverted mold cavity. The reasons for the preferred arrangementwill be discussed later.

The base wall 44 of the mold cavity 36 is provided with a plurality ofopenings 50. Bores 52 extending through the partition wall 48 providecommunication between the vacuum chamber 38 and the openings 50. In thepreferred embodiment, several dozen bores 52 of about 0.0625" diameterare provided. It is understood, however, that the number and size of thebores 52 can be varied without departing from the present invention.

A plurality of temperature control lines 54 extend longitudinallythrough the partition wall 48 and through aligned portions of the lowermold body 30 adjacent the parting line 34.

A gasket 56, preferably formed of high temperature PTFE material, ispositioned in an annular recess 58 which extends along the periphery ofthe base wall 44 at the junction of the base wall 44 and side wall 40 ofthe mold cavity 36. The gasket 56 surrounds the openings 50 in the basewall 44 and the bores 52 and the partition wall 48.

To initiate the production, a sheet 60 of semirigid material, preferablyaluminum, is die cut to an elongated, generally rectangular shape. Theshape of the cut sheet 60 is identical to the desired shape of the topdeck of the completed ski. As shown in FIG. 2, the peripheral shape ofthe cut sheet 60 is substantially identical to the peripheral shape ofthe gasket 56.

The cut sheet 60 is placed in the mold cavity 36 and pressed firmly intoabutment with the base wall 44. The peripheral edge of the sheet 60 isaligned with the peripheral edge of the gasket 56 so that the sheet 60seats on the gasket 56. A vacuum source (not shown) in communicationwith the vacuum chamber 38 is activated, preferably by a foot switch(not shown), to draw a vacuum in the vacuum chamber 38. Preferably,about 25 inches of vacuum are drawn. Vacuum pressure acts through thebores 52 and base wall openings 50 to pull the sheet 60 against the basewall 44, thereby creating a tight seal between the sheet 60 and gasket56. The recess 58 in the partition wall 48 is sufficiently deep so thatthe top surface of the sheet 60 abuts flatly against the cavity basewall 44.

It is appreciated that the vacuum pressure sealing the sheet 60 againstthe gasket 56 could be provided in alternative ways. For example, thevacuum chamber 38 could be located remote from the mold body 32 so longas means were provided for placing the vacuum chamber in communicationwith the base wall openings 50. The means for communication need not bebores extending through the partition wall. An alternative communicationmeans would be pipes or conduits extending outside the mold body 32.

Alignment of the sheet 60 with the gasket 56 can be facilitated byproviding one or more alignment pins 57 on the mold body 32. It isunderstood, however, that the pins are not essential and that alignmentcan be obtained by trial-and-error manipulation of the sheet 60 withinthe mold cavity 36.

The sheet 60 is preferably treated so as to enable foamed plastic to bebonded to the sheet 60 as the plastic is foamed and hardened. Methodsfor pretreating aluminum are described in detail in the above-cited U.S.Pat. No. 4,250,585.

After the sheet 60 is treated, positioned and sealed against the gasket56, the mold 28 is closed by bringing adjacent surfaces of the moldbodies 30 and 32 into abutment with each other along the mold partingline 34. The molding process to use the present apparatus is now readyto commence.

The molding process is basically a reaction injection molding process.Any of the well known plastic foam-producing materials are injected intothe mold cavity 36 through one or more inlets in the mold (not shown)and trapped air is allowed to escape through a suitable vent (notshown). Suitable foam materials and auxiliary agents are discussed inthe above-cited U.S. Pat. No. 4,250,585. Poylurethane foam is thepreferred material for use in the present invention.

The plastic enters the mold cavity 36 in a liquid state. Hence, itinitially rests upon the upper surface of the lower mold body 30 anddoes not come into contact with the sheet 60. However, the ingredientsquickly react to produce a rapidly expanding foam which fills the moldcavity 36. The blowing action of the foam generates internal pressurewithin the cavity 36 which further urges the aluminum sheet 60 againstthe cavity base wall 44 to create an even tighter seal between the sheet60 and the gasket 56.

The expanding foam comes into contact with the bottom surface of thesheet 60 and migrates up along the peripheral edge of the sheet 60. Theseal between the sheet 60 and the gasket 56 prevents the foam frommigrating onto the top side surface of the sheet 60. The foam is thenhardened to produce a dense foam body having a tough skin or crust andhaving the sheet 60 bonded thereto. Selection of suitable moldingconditions of time, temperature and pressure are within the skill of theart.

If desired, the foamed plastic body can be reinforced with internalstructural parts such as steel rods and plastic clips. A method andapparatus for forming such a reinforced body is described in theabove-cited U.S. Pat. No. 4,250,585, and it is recognized that suchmethod and apparatus can be used in the present invention.

The reason for preferring use of the inverted mold cavity shown in FIG.3 can now be readily understood.

A tight seal must be established between the sheet 60 and the gasket 56before the foam material comes into contact with the sheet 60 or elsethe extreme mold pressures will cause the foam material to leak aroundand distort the sheet 60. If the sheet were positioned at the bottom ofa non-inverted cavity, the injected liquid material would flow to thebottom of the cavity and come into contact with the sheet before theonset of foaming. Hence, the vacuum force acting on the sheet would haveto be alone sufficient to seal the sheet against the gasket and preventthe liquid from flowing between the sheet and the gasket. By positioningthe sheet 60 at the top of an inverted mold cavity 36, as is done in thepresent invention, the injected material does not come into contact withthe sheet 60 until it becomes well foamed. At that point, the sheet 60is urged into sealing contact with the gasket 56 by a combination of thevacuum force and the internal pressure generated by the foaming process.Hence, a tight seal between the sheet 60 and gasket 56 is more readilyassured at the critical time.

When the molding process is complete, the mold bodies 30 and 32 areseparated from each other along the parting line 34 and the moldedproduct is removed from the mold cavity 36. The product is a completedwater ski having a foamed plastic body and an aluminum top deck.

The water ski produced by the present invention has a number of featureswhich are not possible in water skis produced by prior art methods.

In the present invention, the deck sheet 60 is narrower than the moldcavity 36 and is positioned along the flat base wall 44 of the moldcavity 36. The side wall 40 of the cavity 36 curves outwardly beyond theperipheral edges of the sheet 60. As a result, the ski has a radiusedtop edge of foamed plastic around the deck sheet 60, as shown in FIG. 3.

In contrast, the prior art process uses a deck sheet which is wider thanthe mold cavity and which is positioned at the mold parting line duringthe molding process. The junction between the sheet and the side wall ofthe mold cavity is a sharp corner. As a result, a ski produced by theprior art process will necessarily have a flat top and a deck extendingcompletely across the top.

Another unique feature in skis produced by the present invention is thatthe top deck 60 is recessed in the foamed body. Referring to FIG. 3, itcan be seen that the top surface of the sheet 60 abuts flatly againstthe cavity base wall 44 and is substantially coextensive with the cavityside wall 40. The foam expands along the side wall 40 until it comesinto contact with the peripheral edge of the sheet 60. Hence, the decksheet 60 is recessed in the foam body and the top surface of the decksheet 60 is flush with the surrounding portions of the foamed body.

In contrast, the prior art process positions the deck sheet outside ofthe mold cavity during the molding process. The expanding foam in themold cavity contacts only the bottom surface of the deck sheet. Hence,the ski has a deck which sits atop the foam ski body.

While the invention has been described with reference to specificembodiments, the exact nature and scope of the invention is defined inthe following claims.

I claim:
 1. Mold apparatus for use in a reaction injection moldingprocess comprising:a first mold body having a mold cavity extending intothe mold body from a parting line with a second mold body, a vacuumchamber formed within the mold body between a base wall of the moldcavity and a base of the mold body, and a partition wall formedintegrally with the mold body and and being disposed between the vacuumchamber and the mold cavity, one of the surfaces of the partition wallforming the base wall of the mold cavity, the base wall of the moldcavity being provided with a plurality of openings extending through thepartition wall providing communication between the vacuum chamber andthe mold cavity, said second mold body separable from the first moldbody at the parting line, a gasket positioned in an annular recessextending along the periphery of the base wall of the mold cavity andsurrounding the plurality of openings, means to provide a vacuum withinsaid vacuum chamber in order to sealingly hold a sheet of semi-rigidmaterial against the gasket and base wall of the mold cavity by saidvacuum provided in the vacuum chamber acting through said plurality ofopenings upon said sheet of material, means for injecting foam producingmaterials into said mold cavity whereby said foam-producing materialsinjected into the mold cavity generate internal pressure within the moldcavity to further urge the sheet material against the gasket and basewall, and whereby after injection the sheet becomes a part of thefinished product.
 2. The apparatus of claim 1 wherein the mold cavityhas curved annular sidewalls spaced inwardly from sides of the moldbody.
 3. The apparatus of claim 1 wherein the size of the sheet materialin area is less than the size of the base wall of the cavity wherebysaid sheet material when held against the base wall of the cavitypermits the foam materials to extend up around the edges of the sheetmaterial.
 4. The apparatus of claim 1 wherein the mold cavity isinverted.
 5. The apparatus of claim 1 wherein a plurality of temperaturecontrol lines extend through the mold body.
 6. The apparatus of claim 1wherein the gasket is formed of high temperature PTFE material.
 7. Theapparatus of claim 1 wherein the peripheral shape of the sheet materialis substantially identical to the peripheral shape of the gasket.